Electrochemical high pressure pump

ABSTRACT

The invention provides electrochemically-based methods and devices for producing fluid flow and/or changes in fluid pressure. In the methods and devices of the invention, current is passed through a divided electrochemical cell. Adjacent compartments of the cell are divided by a separator which comprises an ionically conducting separator. Each compartment includes an electrode and an electrolyte solution or ionic liquid. The electrolyte solution(s) or ionic liquid(s) and the ionically conducting separator are selected to obtain the desired relationship between the current through the cell and the fluid flowrate and/or change in fluid pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/620,457, filed Oct. 19, 2004, which is hereby incorporated byreference to the extent not inconsistent with the disclosure herein.

ACKNOWLEDGEMENT OF GOVERNMENT SUPPORT

This invention was made in part with support under U.S. Army ResearchLab and Research Office Grant DAAD19-03-1-0053. The United StatesGovernment has certain rights in this invention.

BACKGROUND OF THE INVENTION

The invention is in the field of electrochemical pumping of fluids,including electrochemical pumps and methods for inducing pressurizationand/or flow of fluids.

Pressurization and manipulation of fluids on the nano- and micro-scaleare required for a wide range of microfluidics applications includinganalytical and synthetic “lab-on-a-chip”, ultra-small particle handling,and micro/nano-spray systems. Identical demands are key for smartstructures and morphing technologies that incorporate plant-like nasticstructures and/or individually addressable cells (Chopra, I., Amer.Inst. Aeronautics Astronautics J. 2002, 40, 2145; Loewy, R. G., Smart.Mater Struct. 1997, 6, R11). A variety of micropumps have been developedfor these applications. One classification system identifies micropumpsas either displacement pumps or dynamic pumps (Laser, D. J. andSantiago, J. G., 2004, J. Micromech. Microeng., 14, R35-R64).Displacement pumps exert pressure forces on the working fluid throughone or more moving boundaries. Dynamic pumps continuously add energy tothe working fluid in a manner that increases either its momentum or itspressure directly and include ultrasonic, magnetohydrodynamic (MHD),electrohydrodynamic (EHD), electroosmotic or electrochemical actuationmechanisms.

Electrokinetic pumps produce fluid flow through electro-osmosis. Inthese pumps, a dielectric surface is placed in contact with anelectrolyte and an electrically charged diffuse layer extends from thesolid-liquid interface into the bulk of the electrolyte. The applicationof an electric potential to an electrolyte in contact with thedielectric surface produces a net force on the diffuse layer. U.S. Pat.No. 6,572,749, to Paul et al., describes an electrokinetic pumpcomprising at least one tube or channel forming a fluid passagewaycontaining an electrolyte and having a porous dielectric medium disposedtherein between one or more spaced electrodes. An electric potential isapplied between the electrodes to cause the electrolyte to move in themicrochannel by electro-osmotic flow. Silica particles having a diameterof about 100 nm to 6 microns are described as suitable for use as theporous dielectric medium. Ultra micro-porous material such as Vycor®porous glass or a Nafion® membrane was interposed between the electrodeand the high pressure fluid junction. These ultra micro-porous materialsare described as capable of carrying current but having poressufficiently fine that pressure-driven or electro-osmotic flow isnegligible.

The scientific literature describes micro-injectors and micro-dosingsystems based on electrolytic gas generation. Lee et al. describe amicro injector actuated by bubbles generating by the boiling orelectrolysis of an electrolyte in an actuator chamber (Lee, S. W. etal., 1998, Proc. 11^(th) Annual Int. Workshop on Micro ElectroMechanical Systems, Heidelberg, Piscataway, N.J., IEEE). Böhm et al.describe a micromachined dosing system in which the driving force todispense liquids originates from the electrochemical generation of gasbubbles by the electrolysis of water (Böhm, S. et al., 2000, J.Micromech. Microeng., 10, 498-504).

U.S. Pat. No. 4,118,299, to Maget, describes an electrochemical waterdesalination process relying on transport of protons and water through acation exchange membrane. A salt-containing water stream is mixed withhydrogen and then pumped into an electrochemical cell whose anode andcathode are separated by a cation exchange membrane. The electrochemicalcell ionizes hydrogen into protons which migrate to the counterelectrode under the influence of an applied potential. The migratingprotons entrain liquid water. At the counter-electrode, the migratingprotons recombine to form hydrogen while releasing liquid water.

Redox batteries and fuel cells typically involve electrochemical cellcompartments, each compartment containing one or more redox couples. Thecompartments are separated in some cases by an ion selective membrane.Several forms of redox flow cells or batteries have been developed. U.S.Pat. No. 3,996,064 to Thaller describes a two-compartment cell. Duringpassage of current through the cell, an anode fluid is directed throughthe first compartment at the same time that a cathode fluid is directedthrough the second compartment. Chloride salts in aqueous solution aredescribed as useful anode and cathode fluids. U.S. Pat. No. 4,786,567 toSkyllas-Kazacos et al. describes vanadium redox batteries which employV(V)/V(IV) and V(III)/V(II) redox couples.

There remains a need in the art for additional devices and methods forproducing fluid flow and/or pressurization using electrochemical means.

SUMMARY OF THE INVENTION

The invention provides electrochemically-based methods and devices forproducing fluid flow and/or changes in fluid pressure. Theelectrochemical pumps of the invention produce changes in the pressureand/or volume of the electrolyte solution or ionic liquid associatedwith at least one compartment of an electrochemical cell. These pressureand/or volume changes can then be used to drive flow of the electrolytesolution or ionic liquid or flow of an entirely different fluid.

In the methods and devices of the invention, current is passed through adivided electrochemical cell. Adjacent compartments of the cell aredivided by an ionically conducting separator. In an embodiment theionically conducting separator comprises an ionically conductingmembrane. Each compartment includes an electrode and an electrolytesolution or ionic liquid in contact with the electrode. The electrolytesolution(s) or ionic liquid(s) and the ionically conducting separatorare selected to obtain the desired relationship between the currentthrough the cell and the fluid flowrate and/or change in fluid pressure.

The devices of the invention can be sized to produce a variety of flowrates. In different embodiments, the flow rate is between about 1 nL/minto about 1 mL/min or between about 1 μL/min to about 1 mL/min. In anembodiment, only modest voltage/current conditions are required toproduce flow. Some embodiments of the invention require no movingmechanical parts.

Forward and reverse pumping are readily available by changing thedirection of the current through the electrochemical cell. Flexibilityin changing the pumping direction allows repeat sampling and multi-passprocesses. The ability to abruptly change the flow direction can aid influid mixing.

Each electrolyte solution or ionic liquid comprises a redox couple, i.e.soluble chemical species that can be either oxidized at the anode orreduced at the cathode. None of these species or the product produced byoxidation or reduction at the electrodes exists as a gas in theelectrolyte. In the methods of the invention, the electrochemical cellis operated so that the dominant cell reactions are the reactions of theredox couples at the electrodes.

When a potential difference is applied between the cell electrodes,causing passage of electric current through the electrodes, ions andoptionally solvent are tansported across the separator. The separatormay be ion-selective.

The electrochemical cell can be configured so that passage of currentthrough the cell results in an increase in the pressure of theelectrolyte solution or ionic liquid in at least one compartment of theelectrochemical cell. Several mechanisms can lead to the increase inpressure in one compartment, including asymmetric solvent and/or iontransport through the separator, asymmetric changes in the density ofthe electrolyte solutions or ionic liquids caused by changes in apparentmolar volume during the redox reaction, asymmetric changes in thedensity of the electrolyte solutions or ionic liquids caused by changesin apparent molar volume upon ion migration between compartments, andcombinations thereof. The methods and devices of the invention arecapable of producing a liquid pressure in one compartment of anelectrochemical cell of 10 atmospheres or greater. The buildup of fluidpressure in the electrochemical cell compartment can drive flow orspraying of electrolyte solution or ionic liquid from that compartmentor be transferred hydraulically to another compartment.

In an embodiment, the invention provides an electrochemical pumpcomprising

an electrochemical cell comprising

a first compartment comprising a first electrode and a first electrolytesolution, the first electrolyte solution comprising a first redox couplewhich participates in a first electrode reaction and a first group ofions different from the first redox couple species, wherein neither ofthe species of the first redox couple is a gas;

a second compartment comprising a second electrode and a secondelectrolyte solution, the second electrolyte solution comprising asecond redox couple which participates in a second electrode reactionand a second set of ions different from the second redox couple species,wherein neither of the species of the second redox couple is a gas;

an ionically conducting separator separating the first and secondcompartment, the separator being in fluid communication with the firstand second electrolyte solution; wherein the separator allows transportof at least some species of the first and second groups of ions butrestricts transport of the ions of the first and second redox couples;and

a source of electric current connected to the first and secondelectrode;

wherein the pump is configured so that when electric current is passedbetween the electrodes a pressure of greater than 10 atmospheres can beobtained in one compartment.

In another embodiment, the invention provides an electrochemical pumpcomprising

an electrochemical cell comprising

a first compartment comprising a first electrode and a first ionicliquid, the first ionic liquid comprising a first redox couple whichparticipates in a first electrode reaction, wherein neither of thespecies of the first redox couple is a gas;

a second compartment comprising a second electrode and a second ionicliquid, the second ionic liquid comprising a second redox couple whichparticipates in a second electrode reaction, wherein neither of thespecies of the second redox couple is a gas;

an ionically conducting separator separating the first and secondcompartment, the separator being in fluid communication with the firstand second electrolyte solution; and

a source of electric current connected to the first and second electrode

wherein the pump is configured so that when electric current is passedbetween the electrodes a pressure of greater than 10 atmospheres can beobtained in one compartment.

In another embodiment, the electrochemical cell can be configured sothat passage of current through the cell results in an increase in thevolume of electrolyte solution or ionic liquid associated with at leastone compartment of the cell. The same mechanisms that can lead to anincrease in pressure can lead to an increase in volume of electrolytesolution or ionic liquid if the cell is configured to allow flow offluid out of the compartment or if the compartment is not completelyfilled with electrolyte solution or ionic liquid.

Furthermore, the electrochemical cell can also be configured so thatpassage of current through the cell results in an increase in both thevolume and pressure of the electrolyte solution or ionic liquidassociated with at least one compartment of the electrochemical cell.

Changes in the pressure and/or volume of electrolyte solution or ionicliquid associated with one compartment of the electrochemical cell canbe used to induce flow of an external fluid (a fluid other than the cellelectrolytes or ionic liquids) in a flow channel external to theelectrochemical cell. In one embodiment, changes in pressure and volumein one compartment of the cell can be used to drive movement of aflexible diaphragm which forms part of the cell compartment wall. Theflexible diaphragm is in hydraulic communication with the fluid in aflow channel so that movement of the diaphragm induces movement of theexternal fluid in the flow channel.

In an embodiment, the invention provides an electrochemical apparatusfor producing flow of a fluid in a flow channel comprising

an electrochemical pump comprising

a first compartment comprising a first electrode and a first electrolytesolution or ionic liquid, the first electrolyte solution or ionic liquidcomprising a first redox couple, wherein neither of the species of thefirst redox couple is a gas;

a second compartment comprising a second electrode and a secondelectrolyte solution or ionic liquid, the second electrolyte solution orionic liquid comprising a second redox couple, wherein neither of thespecies of the second redox couple is a gas, wherein at least one of thefirst and second compartments further comprises a flexible diaphragm;

an ionically conducting separator separating the first and secondcompartments, the separator being in fluid communication with the firstand second electrolyte solutions;

a source of electric current connected to the first and secondelectrode; and

at least one flow channel containing a fluid; wherein the flow channelis positioned so that the flexible diaphragm is in contact with thefluid in the flow channel

wherein the pump is configured such that when current is passed betweenthe electrodes the pressure in and volume of the electrolyte solution orionic liquid in the compartment having the flexible diaphragm changes,thereby causing movement of the flexible diaphragm and flow of the fluidin the flow channel.

In another embodiment, increases in fluid volume and/or pressureassociated with one compartment of the cell cause outward flow ofelectrolyte solution or ionic liquid through an outlet in thatcompartment. Outward flow of electrolyte solution or ionic liquid can beused to drive flow of an external fluid in the flow channel away fromthe compartment. The outlet is in fluid communication with the flowchannel containing the external fluid. The ionic solution or liquid maybe in direct contact with the external liquid in the flow channel or maybe separated from the liquid by a hydraulic force transmission element.In an embodiment, the hydraulic force transmission element is locatedwithin the flow channel and movement of the hydraulic force transmissionelement in the flow channel induces flow of the fluid. The hydraulicforce transmission element may be gas, liquid, or solid. Similarly,decreases in fluid volume and/or pressure associated with onecompartment of the cell can be used to drive flow of an external fluidin a flow channel towards the compartment.

In an embodiment, the invention provides an electrochemical apparatusfor producing flow of a fluid in a flow channel comprising

an electrochemical pump comprising

a first compartment comprising a first electrode and a first electrolytesolution or ionic liquid, the first electrolyte solution or ionic liquidcomprising a first redox couple, wherein neither of the species of thefirst redox couple is a gas;

a second compartment comprising a second electrode and a secondelectrolyte solution or ionic liquid, the second electrolyte solution orionic liquid comprising a second redox couple, wherein neither of thespecies of the second redox couple is a gas, wherein one of the firstand second compartments further comprises an outlet;

an ionically conducting separator separating the first and secondcompartments, the separator being in fluid communication with the firstand second electrolyte solution;

a source of electric current connected to the first and secondelectrodes;

at least one flow channel containing a fluid, the flow channel being influid communication with the compartment outlet; and

a hydraulic force transmission element located within the flow channelbetween the fluid and the electrolyte solution or ionic liquid from thecompartment with the outlet

wherein the pump is configured such that when current is passed betweenthe electrodes the volume of the electrolyte solution or ionic liquidassociated with the compartment having the outlet changes, therebycausing flow of electrolyte solution or ionic liquid into or out of theoutlet, movement of the hydraulic force transmission element and flow ofthe fluid in the flow channel.

In addition, increases in the pressure and volume of electrolytesolution or ionic liquid associated with one compartment of theelectrochemical cell can be used to pressurize a fluid external to theelectrochemical cell. In an embodiment, the external fluid is in aclosed compartment and a hydraulic force transmission element is locatedin between the electrolyte solution or ionic liquid and the externalfluid.

Furthermore, changes in the pressure and/or volume of electrolytesolution or ionic liquid associated with one compartment of theelectrochemical cell can be used to induce movement of a solid bodyexternal to the electrochemical cell. In one embodiment, changes inpressure and volume in one compartment of the cell can be used to drivemovement of a flexible diaphragm which forms part of the cellcompartment wall. The flexible diaphragm is connected to the solid bodyso that movement of the diaphragm causes movement of the solid body. Thesolid body may act as a hydraulic force transmission element which inturn transfers force to a fluid external to the electrochemical cell.

The invention also provides methods for converting an electric currentor potential to changes in liquid pressure. In an embodiment, theinvention provides a method for converting an electric current to achange in liquid pressure of an electrolyte solution or ionic liquid,the method comprising the steps of:

providing a divided electrochemical cell comprising a plurality ofcompartments, each pair of adjacent compartments being divided by anionically conducting separator, each compartment comprising an electrodeand an electrolyte solution or ionic liquid, each electrolyte solutionor ionic liquid comprising a redox couple, wherein neither of thespecies of each redox couple is a gas and the cell configuration isselected so that passage of an electric current between the electrodesproduces a change in the pressure of the electrolyte solution or ionicliquid in at least one cell compartment; and

passing an electric current between the cell electrodes for sufficienttime that the change in fluid pressure is greater than about 1atmosphere.

The invention also provides methods for producing flow of a fluid in aflow channel. In an embodiment, the invention provides a method forproducing flow of a fluid in a flow channel, the method comprising thesteps of:

providing a divided electrochemical cell comprising a plurality ofcompartments, each pair of adjacent compartments being divided by anionically conducting separator, each compartment comprising an electrodeand an electrolyte solution or ionic liquid and at least one compartmentfurther comprising an outlet, each electrolyte solution or ionic liquidcomprising a redox couple, wherein neither of the species of each redoxcouple is a gas and the cell configuration is selected so that passageof an electric current between the electrodes produces a change in thevolume of the electrolyte solution or ionic liquid associated with thecompartment having an outlet;

providing a flow channel containing a fluid, the flow channel being influid communication with the outlet of the cell compartment; and

passing an electric current between the cell electrodes, thereby causingflow of the electrolyte solution or ionic liquid through the outlet ofthe cell compartment and flow of the fluid in the flow channel.

In another embodiment, the invention provides a method of producing flowof a fluid in a flow channel comprising the steps of:

providing a divided electrochemical cell comprising a plurality ofcompartments, each pair of adjacent compartments being divided by anionically conducting separator, each compartment comprising an electrodeand an electrolyte solution or ionic liquid and at least one compartmentfurther comprising a flexible diaphragm, each electrolyte solution orionic liquid comprising a redox couple, wherein neither of the speciesof each redox couple is a gas and the cell configuration is selected sothat passage of an electric current between the electrodes produces achange in the pressure and volume of the electrolyte solution or ionicliquid in the cell compartment with the flexible diaphragm;

providing a flow channel containing a fluid, the fluid in the flowchannel being in contact with the flexible diaphragm; and

passing an electric current between the electrodes, thereby producingmovement of the flexible diaphragm and flow of the fluid in the flowchannel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Schematic showing an electrochemical pump which produces anincrease in pressure in one compartment of the electrochemical cell.

FIG. 2: Schematic showing an electrochemical pump which produceselectrolyte solution or ionic liquid flow out of one compartment of anelectrochemical cell.

FIG. 3: Fluid pressure as a function of time for an electrochemical cellcontaining electrolyte solutions of tetrapropylammonium iodide andiodine in dimethylformamide (DMF).

FIG. 4 shows the change in fluid pressure with time for electrochemicalcells containing three different electrolyte solutions (LiI/I₂, NaI/I₂,or KI/I₂, all in deionized water).

FIG. 5: Schematic of the electrochemical cell used in the volume changepumping experiment described in Example 3.

FIG. 6: Volume change as a function of charge for electrolysis of 0.5 MTBAI/0.1 M I₂/DMF solutions.

DETAILED DESCRIPTION OF THE INVENTION

The methods and pumps of the invention employ at least one dividedelectrochemical cell. As referred to herein, an electrochemical cellcomprises a container containing two or more electrically conductingphases, each pair of electrically conducting phases being connected byan ionically conducting phase. In a divided cell, the container isdivided into two or more compartments, each containing an ionicallyconducting phase. In an embodiment, the electrochemical cell comprises acell container divided into a first and a second compartment by anionically conducting separator. In another embodiment, theelectrochemical cell may comprise more than two compartments, with eachpair of adjacent compartments divided by an ionically conductingseparator. The cell container may be of any suitable configuration ormaterial known to the art to achieve the desired electrochemicalconfiguration and activity of the cell. The cell container may becompletely rigid, partially flexible, or wholly flexible. Theflexibility of the cell container is selected depending on the desiredmode of operation of the cell. For example, pressure can build up morerapidly in one compartment of the cell if that compartment is rigid. Inanother embodiment, one or more compartments are flexible, allowingexpansion of the compartment.

A source of electric current or electrical potential is connectedbetween the electrically conducting phases of the cell. Sources ofelectric current and electrical potential, such as current and powersupplies, are known to those skilled in the art.

As used herein, the configuration of an electrochemical cell includesthe physical arrangement of the cell, the particular electrolytesolution(s) or ionic liquid(s), and the particular ionically conductingseparator(s). The physical arrangement of the cell includes the numberof cell compartments and whether individual cell compartments containoutlets or other features such as flexible diaphragms. The configurationof the electrochemical pump includes the electrochemical cellconfiguration, as well as the particular electric current or voltagesource selected.

In an embodiment, the electrochemical cell can be adapted or configuredso that the transfer of ions and optionally solvent across the separatorresults in a change in the pressure in the electrolyte solution or ionicliquid in at least one of the cell compartments. In differentembodiments, the pressure in the cell is greater than about 1atmosphere, between about 1 atmosphere and about 10 atmospheres, greaterthan about 10 atmospheres or greater than about 20 atmospheres.

FIG. 1 schematically illustrates a divided electrochemical cell 1 havingtwo compartments 10 a and 10 b, which is configured to allowpressurization of compartment 10 b. Compartments 10 a and 10 b areseparated by ionically conducting separator 20. Compartment 10 a is opento the atmosphere through outlet 12 a and contains electrode 14 a andelectrolyte solution or ionic liquid 16 a. Compartment 10 b is closed,fitted with a pressure transducer 18 and contains electrode 14 b andelectrolyte solution or ionic liquid 16 b. The two electrodes 14 a and14 b are connected through current source 30.The circuit is completed byionic conduction through liquids 16 a and 16 b and ionically conductingseparator 20. Flow of electrons from electrode 14 a to electrode 14 b isaccompanied by a corresponding flow of positive ions from compartment 10a to compartment 10 b. If liquid 16 a is an electrolyte solution, theremay also be a flow of solvent from compartment 10 a to compartment 10 b.Electrolyte solutions or ionic liquids 16 a and 16 b are selected sothat transfer of positive ions (and optionally solvent) from compartment10 a to compartment 10 b results in an increase in the fluid pressure incompartment 10 b.

The change in the fluid pressure in compartment 10 b will depend uponthe pressure change associated with the redox reaction in thiscompartment, as well as the pressure changes associated with ion andsolvent transfer across the separator. If the pressure change associatedwith the redox reaction itself is small, the overall pressure changeassociated with the cell reaction will be dominated by ion and solventtransfer across the separator. In an embodiment, at least one ionspecies having a large apparent molar volume is transported across theseparator from compartment 10 a to compartment 10 b.

In another embodiment, the electrochemical cell is configured so thatthe transfer of ions and optionally solvent across the separator resultsin an increase in the volume of electrolyte solution or ionic liquid onone side of the separator and associated with one of the cellcompartments. An increase in volume of electrolyte solution or ionicliquid causes flow of electrolyte solution or ionic liquid out of thecompartment if the cell compartment is filled with electrolyte solutionor ionic liquid and the volume of the cell compartment is fixed. FIG. 2schematically illustrates a divided electrochemical cell 1 having twocompartments 10 a and 10 b, which is configured to allow fluid flow inor out of compartment 10 b. Compartments 10 a and 10 b are separated byion-conducting separator 20. Compartment 10 a is open to the atmospherethrough outlet 12 a and contains electrode 14 a and electrolyte solutionor ionic liquid 16 a. Compartment 10 b is connected to a flow channel 50through outlet 12 b and contains electrode 14 b and electrolyte solutionor ionic liquid 16 b. The two electrodes 14 a and 14 b are connectedthrough current source 30. The circuit is completed by ionic conductionthrough liquids 16 a and 16 b and ionically conducting separator 20.Electrolyte solutions or ionic liquids 16 a and 16 b are selected sothat transfer of positive ions (and optionally solvent) from compartment10 a to compartment 10 b results in an increase in the electrolytesolution or ionic liquid volume associated with compartment 10 b, whichin turn leads to flow of electrolyte solution or ionic liquid out outlet12 b.

The volume change associated with compartment 10 b will depend upon theapparent molar volume change associated with the redox reaction, as wellas the apparent molar volume change due to ion and solvent transferacross the separator. The volume of electrolyte solution or ionic liquidis referred to as the volume associated with the cell compartment ratherthan the volume in the cell compartment because the volume ofelectrolyte solution or ionic liquid associated with a compartment canbe greater than the compartment volume and therefore may not be confinedto that compartment. For example, if that compartment is filled withfluid, the change in volume may manifest itself as an outward flow offluid from that compartment. If the apparent molar volume changeassociated with the redox reaction itself is small, the overall volumechange associated with the cell reaction will be dominated by iontransfer and optionally solvent transfer across the separator.

The present invention can also be used to drive flow of a fluid in anexternal flow channel, the fluid being other than the electrolytesolution or the ionic liquid in the compartment driving the flow. Inanother embodiment, the cell compartment further comprises a flexiblediaphragm and the cell compartment is filled with electrolyte solutionor ionic liquid. In an embodiment, the flexible diaphragm is impermeableto the ionic solution or liquid. In another embodiment, the diaphragm issemipermeable to the ionic solution or liquid. When the flexiblediaphragm contacts fluid in a flow channel external to theelectrochemical cell, the increase in fluid volume and pressureassociated with the compartment causes deformation of the diaphragm,which in turn can be used to induce flow of fluid in a flow channelexternal to the electrochemical cell. The flow channel may or may not bedirectly connected to the electrochemical cell. Any suitable materialknown to the art may be used for the diaphragm, including polymericmaterials and sufficiently thin sections of non-polymeric materials suchas silicon, glass and metal. The diaphragm material is selected to bechemically compatible with the ionic solution or liquid as well as thefluid in the flow channel.

An electrochemical pump having a flexible diaphragm can be used as areciprocating displacement micropump. Reciprocating displacementmicropumps in which the force-moving moving surface is a deformableplate are known to the art. Several such pumps are described by Laserand Santiago (Laser, J. and Santiago, J. G., 2004, J. Micromech.Microeng., 14, R35-R64) Typically, a reciprocating displacementmicropump comprises a pump chamber bounded on one side by the pumpdiaphragm, an actuator mechanism or driver and two passive checkvalves-one at the inlet (or suction side) and one at the outlet (ordischarge side).

In another embodiment, the flow channel is in fluid communication withan outlet in one of the compartments of the electrochemical cell. Asshown schematically in FIG. 2, the flow channel may be connecteddirectly to the compartment wall. A hydraulic force transmission elementmay be present in the flow channel, located between the electrolytesolution or ionic liquid from the cell compartment and the fluid to bepumped in the flow channel. The hydraulic force transmission element isused to separate the electrolyte solution or ionic liquid from the fluidto be pumped and also to transfer hydraulic force from the electrolytesolution or ionic liquid to the fluid be pumped. In an embodiment, thehydraulic force transmission element may be a gas, such as a bubble. Inanother embodiment, the hydraulic force transmission element may be aliquid. The liquid acting as the hydraulic force transmission elementmay be selected so that mixing is limited between the hydraulic forcetransmission liquid and both the fluid to be pumped in the flow channeland the electrolyte solution or ionic liquid. In an embodiment, theliquid hydraulic force transmission element is selected so that it isimmiscible with and does not react with the fluid(s) to be moved throughthe device. The liquid hydraulic force transmission element is alsopreferably selected so that it wets the flow channel with equal orgreater wettability than the fluid(s) to be moved through the device.These miscibility and wetting conditions allow formation of a “slug” ofliquid between the electrolyte solution or ionic liquid and the fluid inthe flow channel. The viscosity of the liquid hydraulic forcetransmission element is preferably selected so that its resistance toflow can be overcome by the flow of electrolyte solution or ionic liquidfrom the electrochemical cell. In another embodiment, the hydraulicforce transmission element is a solid.

If the cell is configured so that the flow rate of electrolyte solutionor ionic liquid out of the compartment is equal to the transfer of ionsand optionally solvent into the compartment across the separator, theflow rate of electrolyte solution or ionic liquid out of the compartmentwill be constant if the net transfer of ions and optionally solvent intothe compartment across the separator is constant.

In another embodiment, the electrochemical cell is adapted or configuredso that the transfer of ions and optionally solvent across the separatorresults in both an increase in the pressure in the electrolyte solutionor ionic liquid in one of the cell compartments and an increase in thefluid volume associated with that compartment. If the compartment isfilled with electrolyte solution or ionic liquid, the pressure in thecompartment increases if the mechanisms leading to an increase inpressure are not counterbalanced by flow of electrolyte solution orionic liquid out of the compartment or by some other mechanism (e.g.expansion of the compartment). In an embodiment, the cell compartment isfilled with electrolyte solution or ionic liquid and the volume of thecell compartment is fixed. The increase in fluid volume associated withthe compartment causes flow of electrolyte or ionic liquid out of thecompartment. Flow through the outlet is sufficiently restricted that thepressure in the cell compartment increases. The pressure change in thecompartment will depend on the flow rate of electrolyte solution orionic liquid out of the cell, as well as the pressure changes associatedwith the redox reaction and ion and solvent transfer across theseparator.

The current through the electrochemical cell depends on the magnitudeand polarity of the applied potential. In an embodiment, the currentdensity is between about 2 and about 100 mA/cm², where the currentdensity is based on the separator cross-sectional area. Preferably, thecell current is less than the mass-transport limited current associatedwith oxidation or reduction of the redox couple. These current densitiescan be achieved with applied potentials less than about 10 V. In anembodiment, the applied potential is less than about 1 V.

As used herein, an electrolyte solution is a solution containing anelectrolyte. Electrolytes include ionic liquids and chemical compoundsthat dissociate into electrically charged ions when dissolved in asolvent. The solvent is selected so that the electrolyte is soluble andstable in the chosen solvent. The electrolyte solution in adjacentcompartments of the cell may be the same or different. In an embodiment,each compartment of the electrochemical cell contains an electrolytesolution, with the solvent being the same in each compartment. Thesolvent and redox concentrations may be the same in each compartment, ormay be different. In another embodiment, each compartment contains thesame ionic liquid. In an embodiment, at least one compartment containsan electrolyte solution and at least one compartment contains an ionicliquid.

In the present invention, the electrolyte solution or ionic liquidpresent in each compartment comprises a redox couple. As used herein, aredox couple is a pair of chemical species linked by a given halfreaction (either oxidation or reduction) at an electrode. The redoxspecies may or may not be transported across the separator. In addition,some of the redox species may be transported while others are not. Theelectrolyte or ionic liquid may consist essentially of the redox coupleor may comprise additional ionic species. The redox couple in adjacentcompartments may be the same or different.

An “active” redox couple is selected so that under the conditions ofoperation of the cell the predominant electrode reaction is eitheroxidation or reduction of the active redox couple. Determination ofwhether a particular redox couple will be active under given celloperation conditions is known to those skilled in the art. Theelectrolyte solution or ionic liquid may further comprise an additivechelating agent or complexing agent to shift the standard electrodepotential of the redox reaction. The redox couple may be inorganic,organometallic, or organic. Inorganic redox couples include, but are notlimited to (iodide/iodine). Organometallic redox couples include, butare not limited to (ferricyanide/ferrocyanide). Organic redox couplesinclude, but are not limited to (quinone/hydroquinone). In anembodiment, both redox species are ions. In another embodiment, bothredox species are anions. In another embodiment, at least one of theredox species is neutral.

The redox couple is selected so that neither of the species in aparticular redox couple is gaseous under the cell operating conditions.In an embodiment, the current efficiency for any electrode reaction thatproduces a gas is less than about one percent.

Each electrolyte solution or ionic liquid present in a compartment mayfurther comprise an additive which provides additional ions which aredifferent from the redox couple species in that compartment. In anembodiment, at least some of these additional ions are transportedacross the ionically conducting separator. Such an additive may be usedwhen the redox couple species are not transported across the separator,but may also be used when the redox couple species are transportedacross the separator. Useful additive ion species include, but are notlimited to, alkylammonium ions, including tetraalkylammonium ions suchas tetrapropylammonium (TPA⁺) and tetrabutylammonium (TBA⁺), alkalimetal ions such as Li⁺, Na⁺, K⁺, andTRISH⁺(tris(hydroxymethyl)aminomethaneH⁺). In an embodiment, one or moreof the ion species listed above is used in combination with a sulfonatedperfluoropolyethylene cation exchange membrane such as Nafion®.

The redox couples and optional electrolyte or ionic liquid additives areselected in combination with the ionically conducting separator toobtain the desired relationship between the current through theelectrochemical cell and the flowrate and/or change in fluid pressure.The overall change in fluid volume or pressure in a cell compartmentdepends on the combined effect of the volume change associated with theoverall chemical change occurring in the compartment (the overallchemical change being a combination of the redox reaction and ionmigration) and, if applicable, the volume change associated with solventmigration.

The redox reaction may be selected to provide a small change in apparentmolar volume. For example, for the redox reaction I₃ ⁻+2e⁻→3I⁻, theapparent molar volume of I₃ ⁻has been shown to be close to that of 3I⁻insome solutions (Norman et al.,2004, J. Electrochem. Soc., 151(12),E364-D371; Norman et al., 2005, Anal. Chem., 77(10), 6374-6380). In oneembodiment, when an increase in fluid pressure or volume is to beobtained in a particular cell compartment, the redox reaction in thatcompartment is selected so that it does not produce an apparent molarvolume decrease upon reduction.

The species being transported across the separator may also be selectedto have a relatively large apparent molar volume. The ion species isselected to be small enough to allow sufficient transport of the ionspecies across the separator. In an embodiment, the apparent molarvolume of at least one ion species being transported across theseparator is at least about 10 cm³/mol. In other embodiments, theapparent molar volume is at least about 25 cm³/mol, at least about 50cm³/mol, or at least about 100 cm³/mol.

Suitable electrolyte solvents for use with the present invention arethose which allow salvation of the selected redox couples andelectrolyte additives. In an embodiment, the solvents allow theconcentration of the redox couple or electrolyte additive in solution tobe greater than about 0.1 mol/L. These electrolyte solvents include, butare not limited to, water, dimethylformamide (DMF), aqueous organicether mixtures, aqueous acetonitrile, ionic liquids and task specificionic liquids for which the redox couple is part of the ionic liquid.

As used herein, an ionic liquid is a liquid consisting only of anionsand cations. Suitable ionic liquids for use with the present inventioninclude, but are not limited to room temperature ionic liquids, such as1-butyl-3-methylimidizolium tetrafluoroborate.

In an embodiment, the open circuit voltage of the electrochemical cellis zero. As used herein, the open circuit voltage of the electrochemicalcell is the voltage of the cell under zero current conditions. An opencircuit voltage of zero can be achieved by using the same electrolytesolution or ionic liquid in all compartments of the cell. In anotherembodiment, the open circuit voltage of the electrochemical cell isnonzero.

An inert electrode is used that does not take part in any reactionsunder the conditions of the oxidation/reduction of the redox forms.Suitable electrodes for the practice of the invention include graphiteand inert metals such as platinum. In an embodiment, the electrodes arein a form which provides a high surface area. An electrode may also takepart in the redox reaction, for example Ag/AgCI. The electrode materialin adjacent cell compartments may be the same or may be different.

The electrochemical cell compartments are separated by an ionicallyconducting separator. At least a portion of the ionically conductingseparator is ionically conducting. The ionically conducting portion ofthe separator can be a solid or a liquid. In an embodiment, theionically conducting portion of the separator is a membrane. In anembodiment, membranes suitable for use with the present invention forman integral layer and so do not include non-cohesive packed particles.For applications in which development of significant pressures (greaterthan about 1 bar) is desirable, membranes with relatively low hydraulicpermeability are used. Useful membranes with sufficiently low hydraulicpermeability can have pores less than about 100 nm in diameter. Suitableionically conducting membrane materials are well known in the art andinclude hydrocarbon ion exchange membranes, Nafion® (a sulfonatedperfluoropolyethylene sold by DuPont) and other fluorocarbon ionexchange membranes. In an embodiment, the ionically conducting membraneis an ion exchange membrane. Ion exchange membranes may be homogeneousor heterogeneous. In an embodiment, the ionically conducting membrane isa heterogeneous ion exchange resin pressed into a flexible backing, suchas Ionac® (Sybron Chemicals, Inc.) and Ultrex™ (Membranes International,Inc.). In an embodiment, the membrane is a cation exchange membrane.Tonically conducting glasses are also suitable for the practice of theinvention. In an embodiment, the membrane is selected to allowasymmetric solvent transport or an asymmetric change in the density ofthe electrolyte solutions or ionic liquids when current passes throughthe cell. Preferably, the membrane is sufficiently chemically compatiblewith the ionic solution(s) or liquid(s) that any degradation of themembrane by the fluids does not substantially affect transport throughthe membrane during the time period of interest.

The ionically conducting separator is selected to allow a sufficientelectrically-driven flux of the desired ion species through theseparator. The separator may be permselective, so that the flux ofdifferent ion species through the separator differs. In one embodimentwhere ions different from the redox species are added to theelectrolyte, the separator may be used to allow transport of at leastsome of the non-redox ion species but restrict transport of the redoxspecies. In an embodiment, the flux of the redox species is restrictedto be less than about 1%. Use of an ion exchange membrane allowsselection of the sign of the charge of the ions which will betransported across the membrane. For example, the cell may compriseelectrolyte solutions with anionic redox couples and electrolyteadditives which provide cations having a relatively large apparent molarvolume. If a cation exchange membrane is used in the cell, the cationsare the ions which will be transported across the membrane.

When it is desired to transport solvent across the ion permeableseparator, the separator is selected to have a sufficiently hightransference coefficient to produce the desired solvent flow rate acrossthe separator. In different embodiments, the transference coefficient isat least about 3.5, at least about 4, or at least about 5.0. For atleast some ion exchange membranes, the transference coefficient of amembrane for a particular ion/solvent combination correlates with thedegree of solvent swelling of the membrane when the ions are present inthe membrane. Okada et al. have shown that for Nafion® membranes, alkalimetal ions which attract more water molecules in the membrane, which wasreflected as increased solvent swelling, transported more solventmolecules (Okada, T. et al., 2002, J. Phys. Chem. B., 106, 1267).

To increase the pressure of the ionic liquid or electrolyte solution inone of the compartments, the increase in fluid pressure due to thecombination of forward flow of ions and optionally solvent across theseparator and the changes in apparent molar volume for the redoxreaction needs to be greater than the decrease in pressure due to backflow of solvent (and due to the decrease in pressure due to flow out anyoutlets or due to compartment expansion). The rate of backflow ofsolvent through the membrane depends upon its hydraulic permeability.Therefore, the hydraulic permeability of the membrane is another factorin membrane selection when pressurization of the ionic liquid orelectrolyte solution is desired.

For pressurization of the electrolyte solution or ionic liquid in arigid compartment, the energy conversion efficiency can be estimated asenergy conversion efficiency=(V□P)/IEt  Equation 1

where V is the compartment volume, ΔP is the increase in pressure, I isthe current, E is the potential and t is the time (if it can be assumedthat there is no liquid flow out from the pressurized compartment).Mechanisms contributing to loss of efficiency include mechanicalmembrane deformation, backflow through the membrane, and Joule heatingeffects. In an embodiment, the efficiency is greater than about 2%.

A support structure may be used to hold the separator and optionallyreduce its deflection under pressure. The support structure isconfigured to allow contact between the electrolyte solution(s) or ionicliquid(s) and the separator. In an embodiment, the support structure hasan array of holes, the holes being approximately ⅛″ (3.2 mm) indiameter. The support structure may be made of any suitable materialknown to those skilled in the art which is chemically compatible withthe ionic solution(s) or liquid(s).

As used herein, “comprising” is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps. As usedherein, “consisting of” excludes any element, step, or ingredients notspecified in the claim element. As used herein, “consisting essentiallyof” does not exclude materials or steps that do not materially affectthe basic and novel characteristics of the claim. Any recitation hereinof the term “comprising”, particularly in a description of components ofa composition or in a description of elements of a device, is understoodto encompass those compositions and methods consisting essentially ofand consisting of the recited components or elements. The inventionillustratively described herein suitably may be practiced in the absenceof any element or elements, limitation or limitations which is notspecifically disclosed herein.

When a Markush group or other grouping is used herein, all individualmembers of the group and all combinations and subcombinations possibleof the group are intended to be individually included in the disclosure.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments and optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in theart, and that such modifications and variations are considered to bewithin the scope of this invention as defined by the appended claims.Thus, additional embodiments are within the scope of the invention andwithin the following claims.

In general the terms and phrases used herein have their art-recognizedmeaning, which can be found by reference to standard texts, journalreferences and contexts known to those skilled in the art. The precedingdefinitions are provided to clarify their specific use in the context ofthe invention.

All patents and publications mentioned in the specification areindicative of the levels of skill of those skilled in the art to whichthe invention pertains. All references cited herein are herebyincorporated by reference to the extent that there is no inconsistencywith the disclosure of this specification.

EXAMPLE 1 Pressurization in an Electrochemical Cell with DMF ElectrolyteSolutions

Experiments were performed in a two-compartment cell fabricated frompolyetheretherketone (PEEK) with one side open to the atmosphere and theother closed and fitted with a pressure transducer (Micron Instruments,Model MP40A-300A). The membrane was a cation selective ionomer membranecomposed of a perfluorosulfonic acid/PTFE copolymer (Nafion® 117,DuPont) of 180 microns thick and operated with an exposed area of 0.55cm². The membrane was suspended between two ethylene propylene O-ringswith a perforated membrane holder (PEEK) and nylon mesh filter (100micron diameter pore size, Millipore #NY1H) providing mechanicalsupport. Electrical connection was made with platinum mesh electrodes ineach equal-volume compartment (V_(right)=V_(left)=1.25 mL). The pumpingcell was operated in constant-current mode using a galvanostat(Princeton Applied Research, Model 273A) with computer data acquisition(10 Hz acquisition rate: National Instruments DAQcard-6036E, withLabView software).

During pump operation, each compartment was filled with identicalsolutions of tetrapropylammonium iodide (0.5 M; Sigma-Aldrich, >98+%))and iodine (0.25 M, Sigma-Aldrich, 99.8%) in dimethylformamide(Sigma-Aldrich). All chemicals were used without further purification.Initial conditions ensure no concentration difference betweencompartments, effectively eliminating direct osmotic flow contributions.Membranes were conditioned in this solution for 24 to 48 hours andplaced directly into the cell. Operating in the constant-current mode, acurrent applied to the cell of 20 mA resulted in a voltage across thecell of about 5 V.

In forward pumping mode, reduction in the right chamber leads to cationtransport into the right compartment. An increase in pressure isobserved, resulting from cation and solvent flow through the membrane.FIG. 3 shows pressure as a function of time for this system. After ashort induction time, linear pressure behavior is observed with a netforward rate in the presence of backflow of 2.2 atm/min or 2.0 atm/C.With only backflow (at i=0) a reverse rate of 2.3 atm/min is measured at22 atm, indicating an ion-driven forward rate of about twice thepressure-driven back rate (at P_(right)=23 atm, P_(left)=1 atm).Reversible pressure cycling behavior has also been demonstrated.

The energy efficiency for the full pressurization range in FIG. 3, ascalculated rom equation 1, is 3.5%. For the pre-pressurized range above3.5 min, the energy ficiency is 4.1%.

EXAMPLE 2 Pressurization in an Electrochemical Cell with AqueousElectrolyte SolutionS

An electrochemical cell similar to that in Example 1 was used. Duringpump operation, each compartment was filled with identical solutions ofLiI, NaI, or KI (Sigma-Aldrich)) and iodine (0.25 M, Sigma-Aldrich,99.8%) in deionized ultra-high purity water. All chemicals were usedwithout further purification. Initial conditions ensure no concentrationdifference between compartments, effectively eliminating direct osmoticflow contributions. Membranes were conditioned in this solution for 24to 48 hours and placed directly into the cell. Operating in theconstant-current mode, a current applied to the cell of 20 mA resultedin a voltage across the membrane of about 1 V.

FIG. 4 shows a plot of the change in pressure with time for the threedifferent electrolyte solutions (LiI/I₂, NaI/I₂, or KI/I₂). The rate ofchange in pressure with time depended on the iodide salt used. Theapplied current for this figure is as follows: during the first minutethe current was zero, increased to +40 mA at 1 minute, set to zero atminute 3, to −40 mA at minute 4 and back to zero at minute 6.

EXAMPLE 3 Liquid Flow in an Electrochemical Cell with DMF Solutions

Volume changes resulting from electrolysis of DMF solutions are reportedby Norman et al. (2004, J. Electrochem. Soc., 151(12), E364-D371). Aglass electrochemical cell was constructed from two identical L-shapedtubes that were water-jacketed to maintain constant temperatures. Thetwo sides of the cell were assembled with a Nafion® membrane sandwichedbetween two sulfur-cured ethylene propylene (EPDM) O-rings (80 in FIG.5). One side of the cell was capped and the other side was open. FIG. 5shows a schematic of the electrochemical cell. The membrane area thatwas exposed to solution was 5.07 cm².

Initial conditions ensure no concentration difference betweencompartments (approximately 60 mL each), effectively eliminating directosmotic contributions to transport. The solutions were magneticallystirred and large platinum mesh electrodes (approximately 95 cm²) wereinserted in each compartment. A Princeton Applied Research model 173galvanostat was used to control current.

In order to monitor volume changes in the closed compartment, a smallTeflon tube (i.d. 1.06 mm) was connected from the closed compartment ofthe cell to a solution reservoir on a top loading balance above thecell. Volume changes in the closed compartment were determined by themass change in the solution reservoir (and the electrolyte solutiondensity, which was 0.99 g/cm³).

The solutions were of a mixture of 0.5 M tetrabutylammonium iodide(TBAI) from Aldrich at 99% purity or tetrapropylammonium iodide (TPAI)from Aldrich at 98% purity and 0.1 M I₂ from Aldrich in ACS grade DMF.The same electrolyte solution was added to both compartments of thecell.

The positive charge values in FIG. 6 depict how the volume ofelectrolyte solution in the closed compartment of the cell varied as I₃⁻was reduced to I⁻ and TBA+ions migrated across the Nafion® membrane, asa function of the charge passed during the electrolysis. Theexperimental conditions were as follows: Nafion® 117 membrane, 0.5 MTBAI/0.1 M I₂/DMF, 100 mA, Δh=12 cm. The volume-to-charge ratio (cm³/C)was calculated from the slope of a regression line, and a volumetricpumping rate (cm³/s) was calculated from the cell current. For currentsin the range 50-125 mA, the pumping rate was in the range from roughly20 to 50 μL/min.

When the polarity of the electrodes was reversed (negative charge valuesin FIG. 6), I⁻ was oxidized to I₃ ⁻ in the closed compartment and TBA⁺ions and solvent flowed through the membrane into the open compartment,resulting in negative volume changes. The electrochemical pumping couldbe repeated for many cycles.

EXAMPLE 4 Liquid Flow in an Electrochemical Cell with Aqueous Solutions

An acrylic electrochemical cell was constructed from two identicalcylindrical tubes that contained a membrane holder between the twocompartments (Norman et al., 2005, Anal. Chem., 77(10), 6374-6380). Allfittings and valves in this cell design were nonmetallic and composed ofeither PEEK or nylon.

The electrolyte solutions used were one of four iodide salts (LiI, NaI,KI, TrisHI) at a concentration of 1.0 M. The solutions also containediodine (0.1 M) which reacts with excess iodide ion to form triiodideion. Each compartment of the cell contained about 20 mL of solution.

These electrolyte solutions undergo electrolysis, which interconvertsthe iodide and triiodide in the compartments of the cell and drivescations across the Nafion® membrane to maintain electroneutrality.Electrolysis occurred at porous reticulated vitreous carbon electrodes(Electrolytica, Inc., 30 pores per inch; 97% void space) in eachcompartment; these electrodes filled about 90% of the interior volume ofthe cell. Glassy carbon rods inserted in the side of the cell providedthe electrode connection through pressure contact. A Princeton AppliedResearch Model 173 Galvanostat was used to control current.

A series of Nafion® membranes were obtained from the DuPont Company.These membranes were characterized previously by Manley et al. (Chem.Mater. 1996, 8, 2595-2600). Nafion® N002 (EW 1300, dry thickness 125microns) and Nafion® N004 (EW 1500, dry thickness 125 microns) wereexamined for solvent uptake as described above and compared with Nafion®117 (EW 1100, dry thickness 175 μm) membranes in electrolysisexperiments.

In order to monitor volume changes in the compartments, a syringe barrelwas connected to the top of each compartment of the cell through aLuer-loc™ fitting (Becton, Dickinson and Company). The barrels used were50, 100 or 500 μL depending on the electrolyte being investigated andthe total charge passed during electrolysis. Most electrolysisexperiments were conducted for a total charge of 100 C in each directionat constant currents ranging between 25-75 mA. This corresponded tocurrent densities based on exposed membrane area of 10-30 mA/cm². Theliquid volume level in each syringe and the corresponding amount ofcharge passed was recorded periodically. The measured flow rates werereproducible to 10% relative standard deviation or less.

Most of the electrochemically driven flow rates reported below wereobtained by recording fluid levels in syringe barrels attached to thecell compartments. In order to demonstrate that this type of cell couldbe used for flow injection analysis or particle counting applications, afew experiments were performed that used the ports where the syringebarrels usually reside to force flow through a 0.53 mm ID capillary tube(100 cm in length) instead. Flow rate was determined by weighing thesolution that exited the tube and its density. Experiments using theTrisHI/I₂ electrolyte at 75 mA produced flow rates that were within 10rel % of the values determined by volume. For the 0.53 mm ID tubing, thelinear velocity of solution in the tube was approx. 1 mm/s.

The volume-to-charge ratio (μL/C or mL/mol of electrons) for eachelectrolyte was calculated from the slope of the regression line and avolumetric pumping rate (μL/s) was calculated from the cell current(Table 1). For the cations examined the change in membrane materialproduced a relatively small change in flow rate, i.e. flow ratedecreased by 20-50% as the equivalent weight of the membrane increasedfrom 1100 to 1500 g/mol sites. The volume-to-charge ratios in Table 1did not depend upon the current density over the range examined (10-30mA/cm² of membrane), i.e. the fluid pumping was directly proportional tothe cell current. In order to convert the data into more traditionalpumping units, Table 1 also contains volume/time flow rates for thisrange of current densities and the electrolyte/membrane systemsexamined. Pumping rates ranging from less than 1 μL/min to ca. 14 μL/minwere attainable for these operating conditions.

At any time during an electrolysis experiment, reversing the polarity ofthe electrodes caused the flow of electrolyte to reverse directions.Current/flow reversal was repeated many times to insure repeatability ofthe pumping rates.

TABLE 1 Comparison of electrochemical pumping rates for differentelectrolyte cations and Nafion ® membrane materials. Flow rate rangesassume a range of current densities from 10-30 mA/cm² of membrane area.The measured flow rates were reproducible to 10% relative standarddeviation or less. Flow Rate Volume pumped Volume pumped Range Membrane(μL/C) (cm³/mol e−) (μL/min) N117 Li⁺ 2.3 220 3.4-10. Na⁺ 1.5 1502.3-7.0 K⁺ 1.0 93 1.4-4.3 TrisH⁺ 3.1 3.0 × 10² 4.6-14  N002 Li⁺ 1.8 1702.7-8.0 Na⁺ 1.2 110 1.8-5.3 K⁺ 0.6 62 1.0-2.9 TrisH⁺ 2.6 250 3.9-12 N004 Li⁺ 1.5 140 2.2-6.7 Na⁺ 1.0 96 1.5-4.5 K⁺ 0.5 48 0.75-2.2  TrisH⁺2.4 230 3.6-11 

1. An electrochemical pump comprising: an electrochemical cellcomprising a first compartment comprising a first electrode and a firstelectrolyte solution, the first electrolyte solution comprising a firstredox couple which participates in a first electrode reaction and afirst group of ions different from the first redox couple species,wherein neither of the species of the first redox couple is a gas; asecond compartment comprising a second electrode and a secondelectrolyte solution, the second electrolyte solution comprising asecond redox couple which participates in a second electrode reactionand a second set of ions different from the second redox couple species,wherein neither of the species of the second redox couple is a gas; anionically conducting separator separating the first and secondcompartment, the separator being in fluid communication with the firstand second electrolyte solution; wherein the separator allows transportof at least some species of the first and second groups of ions butrestricts transport of the ions of the first and second redox couples;and a source of electric current connected to the first and secondelectrode; wherein the pump is configured so that when electric currentis passed between the electrodes a pressure of greater than 10atmospheres can be obtained in one compartment.
 2. The pump of claim 1wherein the ionically conducting separator is an ion exchange membrane.3. The pump of claim 1, wherein the compartment in which a pressuregreater than 10 atmospheres can be obtained further comprises a closableoutlet.
 4. An electrochemical pump comprising: an electrochemical cellcomprising a first compartment comprising a first electrode and a firstionic liquid, the first ionic liquid comprising a first redox couplewhich participates in a first electrode reaction, wherein neither of thespecies of the first redox couple is a gas; a second compartmentcomprising a second electrode and a second ionic liquid, the secondionic liquid comprising a second redox couple which participates in asecond electrode reaction, wherein neither of the species of the secondredox couple is a gas; an ionically conducting separator separating thefirst and second compartment, the separator being in fluid communicationwith the first and second electrolyte solution; and a source of electriccurrent connected to the first and second electrode wherein the pump isconfigured so that when electric current is passed between theelectrodes a pressure of greater than 10 atmospheres can be obtained inone compartment.
 5. The pump of claim 4 wherein the ionically conductingseparator is an ion exchange membrane.
 6. The pump of claim 4, whereinthe compartment in which a pressure greater than 10 atmospheres can beobtained further comprises a closable outlet.
 7. An electrochemicalapparatus for producing flow of a fluid in a flow channel comprising: anelectrochemical pump comprising a first compartment comprising a firstelectrode and a first electrolyte solution or ionic liquid, the firstelectrolyte solution or ionic liquid comprising a first redox couple,wherein neither of the species of the first redox couple is a gas; asecond compartment comprising a second electrode and a secondelectrolyte solution or ionic liquid, the second electrolyte solution orionic liquid comprising a second redox couple, wherein neither of thespecies of the second redox couple is a gas, wherein at least one of thefirst and second compartments further comprises a flexible diaphragm; anionically conducting separator separating the first and secondcompartments, the separator being in fluid communication with the firstand second electrolyte solutions; a source of electric current connectedto the first and second electrode; and at least one flow channelcontaining a fluid; wherein the flow channel is positioned so that theflexible diaphragm is in contact with the fluid in the flow channelwherein the pump is configured such that when current is passed betweenthe electrodes the pressure in and volume of the electrolyte solution orionic liquid in the compartment having the flexible diaphragm changes,thereby causing movement of the flexible diaphragm and flow of the fluidin the flow channel, and wherein the pump is configured so that apressure of greater than 10 atmospheres can be obtained in thecompartment having the flexible diaphragm.
 8. The apparatus of claim 7wherein the ionically conducting separator is an ion exchange membrane.9. The apparatus of claim 7, wherein the compartment comprising theflexible diaphragm can be configured so that flow of the electrolytesolution or ionic liquid into or out of the compartment can occur onlythrough the ionically conducting separator.
 10. An electrochemicalapparatus for producing flow of a fluid in a flow channel comprising: anelectrochemical pump comprising a first compartment comprising a firstelectrode and a first electrolyte solution or ionic liquid, the firstelectrolyte solution or ionic liquid comprising a first redox couple,wherein neither of the species of the first redox couple is a gas; asecond compartment comprising a second electrode and a secondelectrolyte solution or ionic liquid, the second electrolyte solution orionic liquid comprising a second redox couple, wherein neither of thespecies of the second redox couple is a gas, wherein one of the firstand second compartments further comprises an outlet; an ionicallyconducting separator separating the first and second compartments, theseparator being in fluid communication with the first and secondelectrolyte solution; a source of electric current connected to thefirst and second electrodes wherein the pump is configured so that whenelectric current is passed between the electrodes a pressure of greaterthan 10 atmospheres can be obtained in one compartment; at least oneflow channel containing a fluid, the flow channel being in fluidcommunication with the compartment outlet; and a hydraulic forcetransmission element located within the flow channel between the fluidand the electrolyte solution or ionic liquid from the compartment withthe outlet wherein the pump is configured such that when current ispassed between the electrodes the volume of the electrolyte solution orionic liquid associated with the compartment having the outlet changes,thereby causing flow of electrolyte solution or ionic liquid into or outof the outlet, movement of the hydraulic force transmission element andflow of the fluid in the flow channel.
 11. The apparatus of claim 10,wherein the hydraulic force transmission element is adapted to movewithin the flow channel and is selected from the group consisting of agas bubble, a slug of a second liquid, or a solid.
 12. The apparatus ofclaim 10 wherein the ionically conducting separator is an ion exchangemembrane.
 13. A method for converting an electric current to a change inliquid pressure of an electrolyte solution or ionic liquid, the methodcomprising the steps of: providing a divided electrochemical cellcomprising a plurality of compartments, each pair of adjacentcompartments being divided by an ionically conducting separator, eachcompartment comprising an electrode and an electrolyte solution or ionicliquid, each electrolyte solution or ionic liquid comprising a redoxcouple, wherein neither of the species of each redox couple is a gas andthe cell configuration is selected so that passage of an electriccurrent between the electrodes produces a change in the pressure of theelectrolyte solution or ionic liquid in at least one cell compartment;and passing an electric current between the cell electrodes forsufficient time that the change in fluid pressure is greater than about10 atmospheres.
 14. The method of claim 13 wherein the current isapplied for less than about 5 minutes.
 15. The method of claim 13wherein the current is produced by application of a potential differencebetween the electrodes of less than about 1 V.
 16. A method forproducing flow of a fluid in a flow channel, the method comprising thesteps of: providing a divided electrochemical cell comprising aplurality of compartments, each pair of adjacent compartments beingdivided by an ionically conducting separator, each compartmentcomprising an electrode and an electrolyte solution or ionic liquid andat least one compartment further comprising an closable outlet, eachelectrolyte solution or ionic liquid comprising a redox couple, whereinneither of the species of each redox couple is a gas and the cellconfiguration is selected so that passage of an electric current betweenthe electrodes produces a change in the volume of the electrolytesolution or ionic liquid associated with the compartment having anoutlet wherein the cell is configured so that when an electric currentis passed between the electrodes a pressure of greater than 10atmospheres can be obtained in one compartment; providing a flow channelcontaining a fluid, the flow channel being in fluid communication withthe outlet of the cell compartment; and passing an electric currentbetween the cell electrodes, thereby causing flow of the electrolytesolution or ionic liquid through the outlet of the cell compartment andflow of the fluid in the flow channel.
 17. The method of claim 16,wherein the ionically conducting separator is an ion-exchange membrane.18. The method of claim 16, wherein the flow channel further comprises ahydraulic force transmission element located within the flow channelbetween the fluid and the electrolyte solution or ionic liquid from thecompartment with the outlet.
 19. The method of claim 18, wherein thehydraulic force transmission element is adapted to move within the flowchannel and is selected from the group consisting of a gas bubble, aslug of a second liquid, or a solid.
 20. The method of claim 16, whereinthe current is produced by application of a potential difference betweenthe electrodes of less than about 1 V.
 21. A method of producing flow ofa fluid in a flow channel comprising the steps of: providing a dividedelectrochemical cell comprising a plurality of compartments, each pairof adjacent compartments being divided by an ionically conductingseparator, each compartment comprising an electrode and an electrolytesolution or ionic liquid and at least one compartment further comprisinga flexible diaphragm, each electrolyte solution or ionic liquidcomprising a redox couple, wherein neither of the species of each redoxcouple is a gas and the cell configuration is selected so that passageof an electric current between the electrodes produces a change in thepressure and volume of the electrolyte solution or ionic liquid in thecell compartment with the flexible diaphragm; providing a flow channelcontaining a fluid, the fluid in the flow channel being in contact withthe flexible diaphragm; and passing an electric current between theelectrodes, thereby producing movement of the flexible diaphragm andflow of the fluid in the flow channel wherein the cell is configured sothat a pressure greater than about 10 atmospheres can be obtained in thecompartment comprising the flexible diaphragm.
 22. The method of claim21, wherein the ion-conducting separator is an ion-exchange membrane.23. The method of claim 21, wherein the current is produced byapplication of a potential difference between the electrodes of lessthan about 1 V.
 24. The method of claim 21, wherein the compartmentcomprising the flexible diaphragm is configured so that flow ofelectrolyte or ionic liquid into or out of the compartment can occuronly through the ionically conducting separator.